Most of the institutes use Group Discussions as the next step in the selection process after written examination. That is the reason why Group Discussion has become so very important criteria for selection and rejection of candidates in institutes as well as during campus placements.
GDs are used to assess certain group skills that cannot be evaluated in an interview.
These include reasoning ability, leadership ability, Inspiring ability, flexibility, creativity/out-of-the-box thinking, social skills, listening and articulation skills, situational handling ability, interpersonal ability to function as a team player, body language and attitude.
These are the skills which are very much required to become a successful professional which in turn works as an asset for the institutes at time of campus placements.
Another important reason for institutes to keep GD as an elimination round is because of the crowd factor. At the peak time of admissions, an institute has to deal with 1000s of aspiring students. In a GD, they can analyze up to 15 aspirants in 10 minutes.